Dr. Sudoku Prescribes: Corral

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Dr. Sudoku Prescribes: Corral

Thomas Snyder (aka Dr. Sudoku) is a two-time world sudoku champion and five-time U.S. puzzle champion, as well as the author of several books of puzzles. His puzzles are hand-crafted, with artistic themes, serving as a kind of “cure for the common sudoku.” Each week he posts a new puzzle on his blog, The Art of Puzzles. This week’s prescription deals with Corral puzzles, a mainstay on the United States Puzzle Championship.

The next United States Puzzle Championship will occur later this summer. It is a 2 hour, 30 minute online test that hundreds of American solvers compete in, featuring all sorts of puzzles including observational challenges, loop puzzles and number placement puzzles like sudoku. It has always been a highlight of the puzzle year for me, and I strongly encourage you to check it out when it occurs in August.

For the next several weeks I'll be showcasing puzzle types that might occur on this year's USPC. I'll give a longer write-up, including strategies, on my blog, but will share the puzzle challenges here for practice. This week's topic is Corral, a loop/region-division puzzle that shows up almost every year. This example showcases a few different kinds of logic that you'll need to solve the harder Corral puzzles.

Rules: Draw a single closed loop along the grid lines so that all the numbered squares are inside the loop. Additionally, each number equals the count of interior squares that are directly in line – horizontally or vertically – with that number's square, including the square itself.